The poisoned spear is not equipable and not tradeable, and has no use outside of the quest. Unlike standard poison, there is no way to use karambwan poison in combat.

The poison can be removed with a cleaning cloth, resulting in a tradeable mithril spear.

After completing Tai Bwo Wannai Trio, kp poisoned spears can be bought from Tamayu's Spear Stall. This is nearly useless, because karambwan poison is only able to be used during the quest. Since the store also sells cleaning cloth, this could be used as an easy way to obtain a mithril spear.

The inventory icon for the mithril kp spear uses an old model that no longer looks like a normal mithril spear.

Prior to the Evolution of Combat, karambwan poisoned spears and hastae could be equipped and used in combat. The poison could not be cured by a standard antipoison potion. It would hit a total of 1170 damage before wearing off.